Key Words to Know: (Check off the ones that you know and study the other ones!) Definitions/Related Words

Transcription

1 Unit 7 - Current Electricity Pre-Test Name: ----.J{.a.lE Focus Question for the Unit: How can electron flow be described and manipulated in a circuit? Key Words to Know: (Check off the ones that you know and study the other ones!) Vocab Definitions/Related Words 0 Current 0 Amperes 0 Voltage 0 Volts 0 Resistance I;J Ohm 0 Circuit 0 Resistivity 0 Series 0 Parallel 0 Equivalent Resistance 0 Electrical Power o Electrical Energy Reference Tables: List of Physical Constants (p. 1), Electricity, Circuit Symbols, Resistivities at 20 C (p. 4) 1

2 You will have three minutes to build the following circuit & draw its corresponding schematic. Type of circuit: SERIES or PARALLEL (Circle One) Number of resistors: 2 or 3 (Circle One) Draw the schematic of the circuit below, including the proper placement of the ammeter and voltmeter to measure the total current and total voltage of the entire circuit: 11 Correctly drawn schematic of the circuit 11 Correctly attached ammeter to measure the total amount of current 11 Correctly attached voltmeter to measure the total amount of voltage 11 Correctly attached power supply 11 Correctly attached circuit in either series or parallel BONUS (1 pt): If time remains, you may correctly build the othertype of circuit (ie - if you build a parallel circuit and have time left, you may build a series circuit correctly for an extra point) /5 Total points towards your Unit 7 Exam 2

3 PART 1: Multiple Choice Base your answers to Questions 1 through 3 on the information and diagram below. A 20.-ohm resistor and a 30.-ohm resistor are connected in parallel to a 12-volt battery as shown. An ammeter is connected as shown. 12V ) What is the equivalent resistance of the circuit? t~"i;,ft.+ ~ (1) 10 ohms (2) 25 ohms 012 ohms (4) 50 ohms \;,.~o..ot!.~ 3 2.) What is the current reading of the ammeter? ':1(.'0:.. ~, (1) 1.0 A (2) 0.40 A i.60 A ~) 0.20 A ~ak'"... 1."'\1'''' _--=---_ 3.) What is the power dissipated by the 30 ohm resistor? ~ 0-.8 W (2) 30 W (3) 12 W (4) 75 W 3 4.) In an electric 'field, 0.90 joule of work is required to bring 0.45 coulomb of charge from point A to point B. What is the e~tric potential difference between points A and B?,,: " _ :. T O..'4~c, (1) 5.0 V (2) 0.5~ V ~.O V (4) 0.41 V 2. 5.) What is the resistance at 20 C of a 1.50-meter long aluminum conductor that has a cross-sectional area of 1.13 x 10-6 meter? (1) 1.87 x 10-3 n ~3.74 x 10-2~ ( x 10-2 n (4) 1.33 x 10 6 n 'R-;: 6~~..a'. to 4 ",.~W" A (1.1,\,,10 ",,,, 3 6.) A 330.-ohm resistor is connected to a 5 volt ba ery. The current through the resistor is :r ':.~:. S'v 0 oisa ;,,.,../It " \\0"""-.. (1) ma (2) 335 ma (4) 1,650 ma 2. 7.) An operating electric heater draws a current of 10 amperes and has a resistance of 4 ohms. How much W does the heater use in 3 seconds? (1) 120 J ~200 J (3) 7200 J (4) J ~:. ~"'tt..\: lloa)" l"...){~~) 3

4 _-z. 8.) The diagram below represents an electric circuit consisting of a 12-volt battery, a 3.0-ohm resistor, R 1, and a variable resistor, R Q At what value must the variable resistor be set to produce a current of 1.0 ampere through R1? 12V~ ~ 9.) There is a potential difference of 4 volts across~4 Ii! resistor. What is the power dissipated by the resistor? oft: "", 'I r~..a. (1) 1 watt ([i)4 watts (3) 2 watts (4) 16 watts ~10.) The heating element on an electric stove dissipates 400 Watts of power when connected to a 120 V source. What is the resistance of the heating element? _&- (1) ohms (2) 0.60 ohms", (3) 3.3 ohms R: ~ ': '11.0"1 :: 3"A...., p qoo;:! 1.) Which graph best represents the relationship between potential difference (\I) and current (I) through a single resistor? (1 ) v (3) (4) v v v I I I I ~~ob?! 2.) The current traveling from the cathode to the screen in a TV picture tube is 5.0 x 10-5 Amps. How many electrons strike the screen in 5.0 seconds? (1)3.1x10 24 e ~1.6x1015e (3)6.3x10 18 e (4)1.0x10 5 e %,al. \:%i::: (S')Cto "A)lss): '\0"""(.,. '&.'4\ ':. 2. t.c..to C. 3.) As the cross-sectional area (thickness) of a wire increases, its resistance (1) (3) remains the same It ) A 20 n resistor has 40 Coulombs of charge passing through it in 5.0 seconds. What is the potential difference across the resistor? (1)8.0V (2)1.0x10 2 V.6X10 2 V (4)2.0x10 2 V '2:=1.:. 'O~ ;: ia,,:'%'tlsll"~10.ta.) : ItoO\I ~ 5~ -- 4

5 ~ v ~ 5.) An electric heater operating at 120. vglts draws ~IQO amperes of current through its ft ohms of resistance. The total amount of heat energy produced by the heater in 60.0 seconds is ANV 0 F 'THESE EONS ~ori(: ~a ~t,:%1.rt'ylrt: ('1' 7.20 x 10' J.76 X 10' J (3) 8.64 x 10' J (4) 6.91 x 10' J R. e re~ ~''t1\: (n.o~~'a~w)s): '"4"00'3"' _-z.. 6.) A charge of 30. coulombs passes through a 24-ohm resistor in 6.0 seconds. What is the current through the resistor? "% a ~: loe. : c.~ (1) 1.3 (3).5 A (4) 4.0 A '\ 17.) Which electrical unit is equivalent to one joule? vi ~ "\.: V c.. (1) volt per meter ~volt per coulomb (2) ampere-volt ~oulomb-volt 18.) A small electric motor is used to lift a 0.50-kilogram mass at constant speed. If the mass is lifted a vertical distance of 1.5 mep in.0 secon s, the \,verage power developed by the motor is p,.!:!.. " 11 II ~ M I. ~W\} (1)0.15W (fij).5w t (3)3.8W S (4)7.5W F~:~= (0.$ ~'. "'Sa.)= If.'" _1 9.) The circuit diagram below represents four resistors connected to a 12-volt source. R, =4.0'~ A 2 := 6.0 n R4 =6.0 '2 What is the total current in the A (2) 2.0 A (3) 8.6 A (4) 24 A 20.) Which graph best represents the relationship between thej1ofe&expended by a resistor that obeys Ohm's Law and the pgtegtjal djfferepce applied to the resistor? I " Potential Difference Potential Difference po1ent~erence (2 ) (3) ~ 5

6 r ) The graph below represents the relationship between the current in a metallic conductor and the potential difference across the conductor at constant temperature. Current VS. Potentia.1 Difference ~-c: (I) l'io.. a.. :::J (.) o Potential Difference M The resistance of the conductor is (1) 1.0 n.o n (3) 0.50 n Part II - Problem Solving: Solve all of the following problems. 22.) The diagram below shows two resistors, R1 and R 2, connected in parallel in a circuit having a 120-volt power source. Resistor R1 develops 150 watts and resistor R2 develops an unknown power. Ammeter A 120-vo It.. in the circuit reads 0.50 ampere. r-----; source ~----, a) Calculate the value of R 1. [Show all work, including the equation and substitution with units.} " u U \I. ''''&Oti Ri... 'W,''W'\. 150W p; ~: (r&o V)\".,. IS'()W A}v\/0./\/'~----' ~2 It Tl [It: '"A.\ T, 2-,,,' %:- '?\ \ 'P \1.0.,.U" ''ad'',...~ b) Calculate the amount of charge passing through resistor R2 in 60. seconds. [Show all work, including the equation and substitution with units. 't: ~t, (O.SA'XC.Ch)= \Oc, 'SON 6

7 ,'ti~~$! 23.) What is the resistance of a piece of nichrome wire at 20 C that is 20 m in length and has a diameter of 5.6 x 10-2 m? [Show all work, including the equation and substitution with units.] f ':ISO X 'O 8A ~ t'":.!.. '& (S. Meo a.) a. & '2,v "" l: ~f \,a. 111_ ~ ci ':. $...,o '".~ A '& ~c'".. 1'f to.o-a.&mi : l).c01"." 'R".L ('Co)&.o 8.n...ft\~'t.QfW\) +--:. eel o O'1...I\.l A (0. 00,.,,\0 ~") 24.) A 6-ohm resistor and a 4-ohm resistor are connected in series with a 6-volt battery in an operating electric circuit. A voltmeter is connected to measure the potential difference across the 6-ohm resistor. In the space below, draw a diagram of this circuit including the battery, resistors, and voltmeter using symbols from the Reference Tables for Physical Setting/Physics. Label each resistor with its value. [Assume,the availability of any number of wires of negligible resistance.] 25.) A 3.50-meter length of wire with a cross-sectional area of 3.14 x 10-6 metef is at 20 Celsius. The current in the wire is 24.0 amperes when connected to a 1.50-volt source of potential difference. a.) Determine the resistance of the wire. v. -. b.) Calculate the resistivity of the wire. [ShOW all work, including the equation and substitution with units.] ~., -.) R.~eJ: I ~ ka : lo.,*'a~~~1.i'hio ~ A L {l5'~ S.'-t Jl '0.A.~ 7

8 26.) Base your answers to the questions below on the information and data table. Three lamps were connected in a circuit with a battery of constant potential. The current, potential difference and resistance for each lamp are listed in the data table. [There is negligible resistance in the wires.] C... rent (A) Potential Difference (V) Rulstanee (0) lamp lamp lamps a) Using the circuit symbols found in the Reference Tables for Physical Setting/Physics, draw a circuit showing how the lamps and battery are connected. -- ~t-a.u\\-...", Col'''' btc.a.ra' \IO~ ~e. ij t\t ~'~. b) What is the potential difference supplied by the battery? \1-:..\1, : ""'~"~ : (aco.,,,, c) Calculate the equivalent resistance of the circuit. [Show all work, including the equation and substitution with units.] a.,.-..,,......!-.j....l"'.l-, t., \ \ "'t \ -~ 14&A. \...."\A. t: : o. O"2.OC\ -...,. -=t -a... I ' ' o.o~.. d) If lamp 3 is removed from the circuit, what would be the value of the potential difference across lamp 1 after lamp 3 is removed?, Son\\ v.,)ou\.l ~ ~. \ \I I~; s., s ~?O"tI\~"'\.l'"-'e...nu.. \ ~ S""\4L~ ~ ~ -.~..~\ ) e) If lamp 3 is removed from the circuit, what would be the value of the current in lamp 2 after lamp 3 is removed? si\1\..,.,..,ld k O. \ \ A~ JR." cion'," ~=:; -A.. ~\~# so\ \. -:C~",-\.,i'hLr! ) 8